Ask Mr. Wizard

A Deep Dive Into The Dynamics of Glycol Chillers


Magnus Johansson — Örebro, Sweden asks,

I have a 30-L (8-gallon) conical stainless fermenter from Grainfather; it’s double walled and has an inlet and outlet connection for pumping in cooling liquid. Right now my liquid comes out from a freezer, where I placed a bucket with 15 liters (4 gallons) of glycol. The freezer maintains the glycol temperature at -15 °C (5 °F), and a submersible pump in the bucket is turned on when the temperature in my fermenter rises 0.1 °C (0.2 °F) above the set temperature on the Grainfather controller.

Is there a recommended glycol temperature for fermenter cooling? I have heard something related to “frost burn” of the beer if the glycol is too cold, but I have no confirmation for that phenomenon.

I currently use a timer from eBay installed between the pump and Grainfather controller to prevent bumpy temperature drops by limiting the pump to running for 10 seconds and then waiting 50 seconds before the pump turns on again (provided that the Grainfather controller is calling for cooling); this method makes the temperature more stable. The advantage of having this cold liquid is that I can easily get the cold crashes down to 2–3 °C (35–38 °F).

Your question brings up several interesting points that could be expanded into deep dives into topics that most homebrewers would not find very useful, so I will avoid spending too much time
Response by Ashton Lewis.